There are at least two basic methods used to ignite combustion mixtures in the prior art. Auto ignition through compression and spark ignition. Today a very large number of spark ignited (SI) engines are in use, consuming a limited fossil fuel supply. A significant environmental and economic benefit is obtained by making combustion engines more efficient. Higher thermal efficiencies for SI engines are obtained through operation with leaner fuel air mixtures and through operations at higher power densities and pressures. Unfortunately, as mixtures are leaned, they become more difficult to ignite and combust. More energetic sparks with larger surfaces are required for reliable operation, for example using multiple spark plugs per cylinder systems or rail-plug igniters. As more energetic sparks are used, their overall ignition efficiency is reduced because the higher energy levels are detrimental to the spark plug lifetime. This needs work. These higher energy levels also contribute to the formation of undesirable pollutants plus the overall reduction in engine efficiency.
Radio frequency (RF) plasma ignition sources provide an alternative to traditional direct current (DC) spark ignition and open the door to more efficient, leaner, and cleaner combustion resulting in associated economic and environmental benefits. One method of generating plasma involves using a RF source and standing electromagnetic waves to generate corona discharge plasma. The prior art uses a RF oscillator and amplifier to generate the required RF power at a desired frequency. RF oscillators and amplifiers can be either semiconductor or electron tube based, and are well known in the art. The RF oscillator and amplifier are coupled to the quarter wave coaxial cavity resonator, which in turn develops a standing RF wave in the cavity at the frequency determined by the RF oscillator and the resonant frequency of the cavity. By electrically shorting the input end of the quarter wave coaxial cavity resonator and leaving the other end electrically open, the RF energy is resonantly stepped-up in the cavity to produce a corona discharge plasma at the open end of the quarter wave coaxial cavity resonator. The corona discharge plasma can function generally as an ignition means for combustible materials and specifically in a combustion chamber of a combustion engine.